A lithography technique to replace the conventional semiconductor lithography technique has been sought in view of miniaturization of semiconductor devices. Nano-imprint lithography exists as one such technique, in which a mold produced by electron beam irradiation is used (for example, refer to Non-Patent Document 1). This technique is capable of manufacturing a design rule on the order of nanometers (for example, refer to Patent Document 1). A schematic of this process is that a fine pattern is formed by pressing a mold in which a pattern of nanometer size is drawn and the mold is transferred to a resist on a substrate. In this process, a thermoplastic resin is used as a resist material.
In the formation of the fine pattern of a mold manufactured by the electron beam irradiation, first, the temperature of a resist is raised to the glass transition temperature or higher, and then the mold is pressed to the resist. In this state, the temperature of the resist is lowered and the resist is hardened. Next, the mold is peeled. Thereby, a pattern can be formed on the substrate.
The mold is the most important component in nano-imprint lithography. This is because the precision of the mold determines the precision of the product. Heat resistivity, durability, and the like are necessary in manufactured molds, and adhesiveness between the substrate and a resist layer, electron beam sensitivity of the resist, dry etching durability, an analog property in which the processed depth can be controlled corresponding to an exposure amount of the electron beam, and the like, are necessary in the manufacturing method for the mold.
In order to solve these problems, a resist such as a positive resist including an alkoxysilane group-included a vinyl-based polymer and a curing catalyst (for example, refer to Patent Document 2), and a resist including an aromatic polyamide and an acid generator (for example, refer to Patent Document 3), for example, have been developed. Further, a method has been proposed in which the dry etching durability of the resist is focused on and the resist layer is formed as a two-layered structure (for example, refer to Patent Document 4). For the analog property, a method of irradiating an electron beam by changing the accelerating voltage within a low accelerating voltage range has been disclosed (for example, refer to Patent Document 5). Numerous techniques applying nano-imprint lithography have been disclosed and, for example, a method of manufacturing a field emission negative electrode equipped with a fine needle shaped electrode (for example, refer to Patent Document 6) has been disclosed.
A conventional fine processing method by electron beam irradiation is performed at a high acceleration voltage of 50 kV or higher, and mostly at 100 kV or higher, as described in Patent Document 2 and Patent Document 3. Together with this, a high irradiation dose (also referred to as a dosage), for example 500 μC/cm2 or more of the irradiation dose, inevitably becomes necessary, and there is even a case in which an irradiation dose of about 105 μC/cm2 is used, which results in, for example, one drawing requiring a long time such that productivity is extremely low. Further, with respect to apparatus, apparatus using a high acceleration voltage is expensive, and energy efficiency is poor due to large power consumption.
The reason for using a high acceleration voltage is that it is effective to produce a pattern where the depth is almost fixed, such as a two-dimensional mold such as a semiconductor, by repeating irradiation of a fine beam corresponding to a desired pattern, because the electron beam is implanted into a substrate penetrating through the resist while keeping a fine beam diameter due to the ease of turning down the diameter of the electron beam and a decreased interaction between the electrons and the resist. However, the sensitivity decreases with the decrease of the interaction, and a high dosage becomes necessary to compensate for this, resulting in the problem that drawing requires a long time.
In this way, conventionally, the prevailing method of fine processing with electron beam irradiation has been the production of a two-dimensional mold pattern, and there have been few examples of application to the production of a 3-D pattern in which height, depth, and line width are changed.
In the case of manufacturing a 3-D pattern, conventionally, a method of increasing and decreasing the irradiation dose by fixing the voltage in the range of the high acceleration voltage, the so-called high acceleration dose modulation method, is also generally used. However, normally, an electron beam resist is sensitive to the change in the irradiation dose and the height, the depth, and the line width change thereby, controllability is low, control of the line width and control of the depth are both at about 50 nm even if the controllability is high, and it is difficult to manufacture a desired 3-D fine pattern.
Furthermore, with this kind of high acceleration voltage, normally, an incident electron passes the resist layer and is implanted into the substrate, and then bounces back in the direction of incidence, scatters over a wide range (referred to as backscatter) and energy is stored in the resist. Particularly, in the case of performing the irradiation at two places, when the mutual irradiation range is narrow, scattering electrons overlap each other (the stored energy is referred to as a proximity effect), and as a result, this energy becomes the cause of disturbance of the precision of processing in the depth direction and/or the width direction of a finely processed pattern.
In particular, because the irradiation dose is changed due to influence of the backscattering electrons, the reproduction of a 3-D fine pattern becomes even more difficult.
Various methods to suppress the effect on a processed pattern dimension by controlling this proximity effect due to the backscattering electrons have been proposed.
For example, in the case of electron beam irradiation fine processing with a high acceleration voltage, since the sensitivity is poor, a method exists of increasing sensitivity in advance by separately performing electron beam irradiation with a low acceleration voltage of about 30 kV and then performing the irradiation with an acceleration voltage of about 100 kV repeatedly (for example, refer to Patent Document 7). However, the correction effect by these methods is insufficient, and these methods have not resulted in obtaining satisfactory processed pattern dimensions.
Therefore, the present inventor has proposed a method of changing the dosage (an irradiation dose) in a high range of about 500 to 10,000 μC/cm2 by fixing the acceleration voltage in the range of a low region in order to control the processed depth of the resist layer, has clarified that the acceleration voltage and the processed depth have almost a proportional relationship by changing the acceleration voltage, particularly by changing the apparent acceleration voltage by changing the voltage of a sample stand side, and has proposed a processing and manufacturing method for a resist and a substrate exhibiting an excellent analog property (for example, refer to Patent Document 8).
However, while with this proposal, the processed depth precision can be improved over the conventional method by a low acceleration voltage and a high irradiation dose, it remains insufficient and, further, the control of the line width of a fine line is performed by adjustment of the electron beam diameter, and a satisfactory line width control has not been obtained.
When the line width control is not based on the adjustment of the electron beam diameter, if the irradiation dose is high, it is also considered to be difficult to control a fine line.
Furthermore, depending on the density of the fine pattern or the spacing of the adjacent pattern, there are many cases in which all of the patterns stick together or are left out, and it is extremely difficult to draw, in particular, the line width of a fine line to a desired dimension.
Moreover, it is proposed in Patent Document 5 that a thin film-type micro-optical element that is excellent in optical characteristics is manufactured by changing a voltage in a range of low acceleration voltage within which the electron beam does not reach the substrate. However, there is no description whatsoever related to the irradiation dose and the processing precision, and it is thought that manufacture of an element with high processing precision cannot be anticipated without performing an adjustment of the irradiation dose, even if it is the same as Patent Document 8 in respect of irradiating an electron beam of low acceleration voltage.
In view of the trends in this kind technological development, a processing technology for a finer mold is required, and the development of an outstanding mold production technology that is capable of manufacturing a line width that is impossible with the conventional lithography method or mechanical processing, which is possible to control to a 10 nm processed depth and that is narrower than 200 nm, is highly sought after.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2002-192500
Patent Document 2: JP-A No. 2002-196494
Patent Document 3: JP-A No. 07-219228
Patent Document 4: JP-A No. 60-263145
Patent Document 5: JP-A No. 62-109049
Patent Document 6: JP-A No. 6-196086
Patent Document 7: JP-A No. 2005-19426
Patent Document 8: International Publication No. 2004/027843 A1
Non-Patent Document 1: S. Y. Chou, P. R. Krauss, and P. J. Renstrom: “Imprint of sub-25 nm vias and trenches in polymers,” Applied Physics Letters 67, pp. 3114-3116 (1995)